As a rule, a 5751 is less microphonic and quieter than a 12AX7, especially when you are comparing a NOS 5751 to current production 12AX7's. It has a higher gain factor than a 12AT7 and I would always suggest trying the 5751 first. If the amp still has noise, then it is probably coming from a non-tube source and you would have to let a tech have a go at it. If you are going to use a 5751, they have NOS one's for sale on "The Tube Store" or "The Tube Depot" and the prices are reasonable. Take care, Marty

Marty do have anymore info on the 5751 as a replacement for the 12AX7? I'm trying to tell if this would make my AVT less noisy or not?